This invention relates to a copier with an automatic exposure control device such that copies with optimum image density can be easily obtained and more particularly to such an exposure control device which varies the exposure in a stepwise fashion to achieve proper exposure.
Since situations occur frequently where the user of a copier wishes to vary light exposure according to the density and kind of the original document to be copied, there have been many copiers developed with various exposure selecting means. With a copier of this type, the user usually presses a print button a number of times to actually obtain copies with different exposures and selects the best one of these many copies having different image densities.
There have also been developed copiers with an automatic exposure control device with which the density of the original document to be copied is automatically detected and the level of exposure is automatically adjusted according to the detected density. Such copiers cannot function properly, however, if the density varies radically, for example, from one end of a document to the other. In such a situation, exposure must be varied manually in a stepwise fashion as explained above. It now goes without saying that it is extremely inconvenient if the user is required to press the print button many times while varying exposure. Some copiers with an automatic density detecting means are also provided with a sensitivity setting means for setting the relationship between the output from the density detecting means indicative of the density of the document to be copied and the exposure to be given to the photoreceptor of the copier. With such a copier, a test document or a document with a standard reference density is provided and a proper level of exposure sensitivity is set by copying such a document. With such copiers, too, the user is required to experiment many times with the adjustment of sensitivity by actually making copies of such a test document.